The main objective of these studies is to determine if cortical stimulation combined with motor rehabilitative therapy will improve motor function following traumatic brain injury (TBI). Motor recovery is thought to be a process of "relearning" in which motor functions are reacquired through functional compensation within spared brain regions. Several laboratories have demonstrated that such functional compensation is supported by synaptic plasticity within residual neural circuits that are driven by rehabilitation. Previous studies in stroke models also strongly indicate that behavioral improvements and cortical plasticity are enhanced by administering cortical stimulation (CS) during motor rehabilitative training (RT). It is often assumed that motor impairments, and thus treatment strategies to alleviate them, are the same between TBI- and stroke-induced motor cortex damage. However, the optimal parameters used for treatment following ischemic stroke and contusion injury are almost certain to vary because they have very different patterns of cellular responses, time-line of behavioral recovery and responsiveness to rehabilitative training. Furthermore, because TBI appears to create an enduring resistance to experience-dependent neural plasticity, it may be that adjunctive treatments that overcome this resistance are especially critical to unleash the potential of behavioral interventions after this type of injury. We hypothesize that effective CS delivered over the contused sensorimotor cortex during rehabilitative training will induce greater behavioral improvements and that these improvements will be supported, at least in part, by enhancement of functionally relevant reorganization of remaining motor cortex. Our recent preliminary data in a rat model of controlled cortical impact (CCI) injury supports the likelihood that CS+RT can be used to improve motor performance after TBI and that this may be a result of its enhancement of motor cortical plasticity. However there is a need to better understand the parameters of CS treatment that maximize its effectiveness for promoting enduring improvements in motor function and to understand the neural basis of effective versus ineffective treatment. The proposed studies will 1) establish optimal stimulation parameters in a rat model of unilateral CCI;2) determine if effective CS enhances the motor cortical structural and functional responses to rehabilitative training and the necessity of the reorganized cortex for the behavioral improvements;3) investigate if there is a sensitive period for the effectiveness of CS-induced improvements;and 4) investigate if CS effects are enduring and if timing of treatment initiation affects CS endurance. We will use a combination of sensitive behavioral measures, quantitative light microscopy to assay changes in markers of neuronal structural plasticity, and intracortical microstimulation (ICMS) mapping to reveal the functional integrity and organization of motor cortex. These investigations are expected to provide support for a potentially powerful treatment option for survivors of traumatic brain injuries. PUBLIC HEALTH RELEVANCE: Cortical stimulation combined with motor rehabilitation may improve motor outcome after traumatic brain injury (TBI). Using an animal model, these studies will establish appropriate stimulation parameters to improve motor performance, test the persistence of improvements and quantify brain reorganization due to treatment. By revealing the neural mechanisms underlying effective versus ineffective CS treatment, these studies will facilitate the future development of assays of treatment efficacy as well as reveal new targets for therapeutic interventions, laying the foundation for future clinical trials using CS to improve motor recovery after TBI.